Incident Charge State Research Articles

Target K-shell X-ray emission associated with single and double electron capture for [formula omitted] + Ar collisions

Cross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the same cross sections corresponding to projectile F K X-rays and the total cross sections for single and double capture, were determined for 1.8–2.2 MeV/u F9+,8+,7+ projectiles. This work was performed at Western Michigan University using the tandem Van de Graaff accelerator. Coincidences between emitted X-rays and their corresponding charge-changed particles were detected. The Ar K X-ray coincidence cross section ratios for double to single capture are found to depend strongly on the incident charge state, with the ratios for F9+ well exceeding unity. Possible explanations for this anomalous behavior are discussed but a conclusive explanation is not found. The results are compared to previous experiments using fully-stripped fluorine where coincidence techniques were not employed.

Single and double electron capture associated with characteristic K-shell X-ray emission for F9+,8+,7++Ar

SynopsisCross sections for target Ar K-shell ionization associated with single and double electron capture, as well as the corresponding cross sections for total electron capture and the projectile F K x rays, were determined for 1.8-2.2 MeV/u F9+,8+,7+ projectiles. The Ar K x-ray coincidence cross section ratios for double to single capture are found to vary strongly with the incident charge state, with the ratios for F9+ well exceeding unity.

The role of radiative de-excitation in the neutralization process of highly charged ions interacting with a single layer of graphene

X-ray emission of slow (<1 a.u.) highly charged Argon and Xenon ions is measured for transmission through a freestanding single layer of graphene. To discriminate against X-ray emission originating from the graphene's support grid a coincidence technique is used. X-ray emission of 75 keV Ar17+ and Ar18+ ions with either one or two K-shell vacancies is recorded. Using a windowless Bruker XFlash detector allows us to measure additionally Ar KLL and KLM Auger electrons and determine the branching ratio of radiative vs. non-radiative decay of Ar K-shell holes. Furthermore, X-ray spectra for 100 keV Xe22+-Xe35+ ions are compared, showing a broad M-line peak for all cases, where M-shell vacancies are present. All these peaks are accompanied by emission lines at still higher energies indicating the presence of a hollow atom during X-ray decay. We report a linear shift of the main M-line peak to higher energies for increasing incident charge state, i.e. increasing number of M-shell holes.

Additivity of kinetic and potential energy contributions in modification of graphene supported on [formula omitted

The damage production induced by MeV highly charged ions (HCI) irradiations in graphene supported on a SiO2 substrate is investigated using molecular dynamics method. We get results in agreement with our recent experiments. We find that the electronic energy loss and potential energy deposition have similar effects on the defects creation in SiO2 substrate-supported graphene and both mechanisms of energy deposition seem to contribute in an additive way. The influences of the energy deposition depth and radius are studied. Only the energy deposited below the surface within 2.5nm will induce the damage in graphene. Hence, the HCI can be a powerful tool to induce defects in graphene without causing deep damage of the substrate. When charge of incident Xeq+ is above 30, a nanopore is formed and the size of nanopore in graphene can be controlled by changing the incident charge state.

Incident ion charge state dependence of the visible light emission of Xeq+ ions bombarding aluminum

AbstractIn this work, we studied the photon emission in the visible light range for Xeq+ ions of different charge states (10 ≤ q ≤ 21) bombardment on an aluminum target at 410 keV. During the interactions, the spectra in wavelength range 300–500 nm are recorded, including the photons from Al atoms and neutralized Xe+ ions. The yield of the visible light strongly depends on the projectile charge states. Its variation tendency with the charge states is similar to that of the potential energy variation. In addition, the experimental results also indicate that when the incident charge state is less than the critical charge state, it obeys the staircase classical-over-barrier model.

Dynamic evolution of 100-keV H+ through polycarbonate nanocapillaries

In recent years, the guiding effect of highly charged ions (HCIs) through insulating nanocapillary membrane has received extensive attention. It is found that slow highly charged ions at keV energies can be guided along the capillary even when the title angle of membrane is a few degrees and larger than geometry opening angle of the capillary. Initially, Stolterfoht et al. (2002 Phys. Rev. Lett. 88 133201), according to the incident ions deposit positive charges on the capillary surface in a self-organizing manner, proposed scattering and guiding regions to explain this guiding phenomenon. Hereafter, a detailed experiment and simulation performed by Skog et al. (2008 Phys. Rev. Lett. 101 223202) provided clear evidence that the guiding process is actually attributed to the self-organized charge patches formed on the inner capillary walls. HCIs entering into a capillary may hit the surface, leaving their charge on the inner wall of the capillary. When the capillary axis is tilted with respect to the beam incidence direction, a charge patch is formed in the capillary entrance, simultaneously a repulsive electric field is created. After sufficient charge deposition this field is strong enough to deflect the subsequent ions in the direction of the capillary exit. Therefore, the ions are guided through the capillary. The deflection at the charge patch only occurs at relatively large distances from the capillary wall so that the incident charge state of the ions is kept during the passage through the capillary. Further experimental and theoretical studies on various target materials, such as polyethylene terephthalate (PET), polycarbonate (PC), SiO2, and Al2O3 indeed found that a single or a small number of charge patches near the entrance formed in the charge up process dominate the observed oscillatory variations of the ion emission angle and the final guiding process. Besides, measurements and simulations of the steering of swift ions at MeV energies have shown that the transmission mechanism of the high energy ions in a tapered tube is primarily dominated by multiple random inelastic collisions below the surface and the charge patches are not responsible for the transmission process. However, the studies of the transmission of hundreds keV ions through nanocapillaries are still lacking so far. In this work, we observe the evolution of the angular distribution, charge state distribution, FWHM and transmission rate of 100 keV H+ ions incident on a polycarbonate (PC) membrane at +1 tilt angle. It is found that the transmitted particles are located around the direction along the incident beam, not along the capillary axis, which suggests that the mechanism of hundreds keV (E/q~100 kV) protons through capillaries is significantly different from that for the guiding effect of keV protons. We present a qualitative explanation based on the data: that the 100 keV H+ are transmitted by multiple random inelastic collisions below the surface is attributed to the absence of the deposited charges on the surface of the capillary at the beginning of the experiment. After the equilibrium, several charge patches are formed on the inner wall of the capillary, which suppresses the ions to penetrate into the surface of the capillary, while the H+ is transmitted via specular scattering above the surface (or closest to the surface) assisted by the charge patches, and finally is emitted in the incident direction through twice specular scattering. This finding increases the knowledge of charged ions through nanocapillaries, which is conducible to the applications of nanosized beams produced by capillaries or tapered glass within hundreds keV energies in many scientific fields.

Interaction of highly charged ions with carbon nano membranes

Charge state and energy loss measurements of slow highly charged ions (HCIs) after transmission through nanometer and sub-nanometer thin membranes are presented. Direct transmission measurements through carbon nano membranes (CNMs) show an unexpected bimodal exit charge state distribution, accompanied by charge exchange dependent energy loss. The energy loss of ions in CNMs with large charge loss shows a quadratic dependency on the incident charge state, indicating charge state dependent stopping force values. Another access to the exit charge state distribution is given by irradiating stacks of CNMs and investigating each layer of the stack with high resolution imaging techniques like transmission electron microscopy (TEM) and helium ion microscopy (HIM) independently. The observation of pores created in all of the layers confirms the assumption derived from the transmission measurements that the two separated charge state distributions reflect two different impact parameter regimes, i.e. close collision with large charge exchange and distant collisions with weak ion-target interaction.

Double effects of projectile charge state on Nb L-shell ionization by slow highly ionized Xe ions

Nb L-shell ionization cross sections induced by Xeq+ (12 ≤ q ≤ 29) ions were measured as a function of the incident charge state q in the energy ranging from 1500 to 2500 keV. In this experiment, w...

Charge exchange and energy loss of slow highly charged ions in 1 nm thick carbon nanomembranes.

Experimental charge exchange and energy loss data for the transmission of slow highly charged Xe ions through ultrathin polymeric carbon membranes are presented. Surprisingly, two distinct exit charge state distributions accompanied by charge exchange dependent energy losses are observed. The energy loss for ions exhibiting large charge loss shows a quadratic dependency on the incident charge state indicating that equilibrium stopping force values do not apply in this case. Additional angle resolved transmission measurements point on a significant contribution of elastic energy loss. The observations show that regimes of different impact parameters can be separated and thus a particle's energy deposition in an ultrathin solid target may not be described in terms of an averaged energy loss per unit length.

Charge-state distributions of fast diatomic carbon ions and dissociated fragments passing through microcapillaries

We measured charge distributions of fast diatomic molecular ions after transmission through microcapillaries. Projectile beams of C2 ions with velocities of 0.89–1.79 au were incident on single-tapered capillaries with two different outlet diameters of 7.7 and 13.7 µm. We found that most of the transmitted primary C2 ions retain their incident charge states. For dissociated C1 fragments resulting from scattering with capillary-wall surfaces, their average charges increase with increasing velocity. The velocity dependence exhibits a similar trend to that of the equilibrium charge of atomic carbon particles that penetrate through matter. It was concluded that the molecular fragmentation during the transmission occurs mainly via grazing scattering at shallow layers below the surface of capillaries.

Secondary electron emission from a thin carbon foil induced by equi-velocity protons and electrons of 0.5–3.5 MeV/u

The statistical distributions of the number of simultaneously forward-emitted secondary electrons (SEs) from a thin carbon foil have been measured with H 0 and H + projectiles of 0.5–3.5 MeV in coincidence with the foil-transmitted protons, irrespective of projectile incident charge state. From these results, the probabilities of the simultaneous emission of n electrons and the SE yields by loss electrons have been evaluated. At energies of 2.5–3.5 MeV, the obtained emission probabilities and the SE yields induced by loss electrons are larger than the corresponding ones by protons of the same velocity. Furthermore, the material parameter is found to be almost constant and is slightly larger than that for the protons. On the other hand, the forward SE yields by loss electrons is decreasing to zero with decreasing the incident energy. This behavior is consistent with the range-energy relation of electrons in carbon.

Energy loss and fragmentation of 3 keV [formula omitted] ions at grazing scattering from a KCl(0 0 1)

Charge state, angular and energy distributions of reflected projectiles are measured when 3 keV C 60 + , 2 + ions are scattered from a clean and flat KCl(0 0 1) surface under grazing incidence. The dominant charge state is found to be C 60 + irrespective of the incident charge state as is expected from the electronic structure of KCl and C 60 ions. The observed angular distribution has a well defined peak at a specular angle, indicating that the normal energy is not dissipated during the grazing angle scattering. In spite of no dissipation of the normal energy we observe the fragmentation of the scattered C 60 + ions. The energy transferred from the parallel energy to the internal excitations was estimated from the observed fragment distribution. The transferred energy changes from almost 0 to ∼15 eV when the angle of incidence changes from 1° to 6°, which is less than 10% of the observed energy loss of the C 60 + ions.

Direct Evidence for Projectile Charge-State Dependent Crater Formation Due to Fast Ions

We report on craters formed by individual 3 MeV/u Au (q(ini)+) ions of selected incident charge states q_(ini) penetrating thin layers of poly(methyl methacrylate). Holes and raised regions are formed around the region of the impact, with sizes that depend strongly and differently on q_(ini). Variation of q_(ini) of the film thickness and of the angle of incidence allows us to extract information about the depth of origin contributing to different crater features.

Projectile charge-state dependence of methane fragmentation

The projectile charge-state dependence of methane fragmentation is studied at a constant projectile (${\mathrm{Ar}}^{q+}$, $1\ensuremath{\le}q\ensuremath{\le}7$) velocity of $0.42\phantom{\rule{0.3em}{0ex}}\text{a.u.}$ using the technique of time-of-flight mass spectroscopy. The relative cross sections for fragment production are reported as a function of the incident projectile charge state. The fragments appearing as molecular ions show a decrease in cross sections with increasing projectile charge state as opposed to the carbon ions which show an increase with increasing projectile charge state.

Dependence of secondary-electron emission on the emergent angle of frozen-chargedH0andH+projectiles penetrating a thin carbon foil

The statistical distributions of the number of secondary electrons (SEs) emitted per projectile from a thin carbon foil under irradiation with the frozen-charged ${\mathrm{H}}^{0}$ and ${\mathrm{H}}^{+}$ projectiles of $2.5--3.5\phantom{\rule{0.3em}{0ex}}\mathrm{MeV}$ have been measured as a function of the emergent angle of projectiles in the range from $0.0\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}2.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ in every $0.5\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ step. The measurement of SEs was carried out in the forward and the backward directions of the incident beam independently. From $0.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$ to $\ensuremath{\sim}1.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$, the SE yields, that is, the mean number of emitted electrons per incident ion, increase with increasing emergent angle and tend to be saturated at larger angles. This is a common trend, regardless of incident energies and charge states of a projectile and also of emitted directions of SEs. Quantitatively, the saturated SE yields at larger angles for the ${\mathrm{H}}^{+}$ penetration are about 40--50 % larger than those at $0.0\phantom{\rule{0.3em}{0ex}}\mathrm{mrad}$. On the other hand, the corresponding relative increase for the ${\mathrm{H}}^{0}$ penetration reaches as high as $\ensuremath{\sim}100%$ or more. The observed proton-hydrogen difference is well reproduced in the calculated energy losses by a Monte Carlo simulation including the impact parameter dependent stopping cross sections in a single collision of a hydrogen or a proton with a carbon atom.

Investigation of the processes in the collisions of partially stripped carbon ions with helium atom at low to intermediate energies

he cross-section ratios for the double-to-single ionization of He associated with no projectile charge change (Rq,q), single-electron capture (Rq,q-1) and single-electron loss (Rq,q+1) were measured using coincidence technique. The coincidences resulted from the signals of recoil ions and scattered projectiles. For a given incoming projectile charge state the double-to-single ionization ratios vary strongly with the outgoing reaction channel. It is found that Rq,qRq,q+1Rq,q-1. For direct ionization, Rq,q is nearly independent of the incident projectile charge state. However, for ionization associated with single-electron capture and single-electron loss by the projectile, Rq,q-1 and Rq,q+1 depend strongly on the incident charge state of the projectile. These ionization ratios are interpreted in terms of theories of the atomic polarization effect and the screening and antiscreening effect of the electrons around the core.

Irradiation by swift heavy ions: Influence of the non-equilibrium projectile charge state for near surface experiments

When dealing with surface and/or thin film modifications of materials under irradiation by swift heavy ions, special attention should be given to the choice the incident projectile charge state delivered by the accelerator. This charge state should be of the order of the effective charge defined in the electronic energy loss theory. Under some hypothesis, this effective charge is assumed to be equivalent to the mean charge state deduced from measurements of ion charge state distribution. To reach such a charge state, it is necessary to introduce before the irradiated sample a thin stripper foil of carbon, the thickness of which is in between ∼5 and ∼1500μg/cm2 for beam energies ranging between 1 and 44MeV/u, respectively.

X-rays emitted from N ions transmitted through a thin Ni microcapillary target

K X-rays emitted from 2.1keV/u N ions transmitted through a thin Ni microcapillary foil were measured in coincidence with a final charge state qf, using a Si(Li) X-ray detector in the cases of incident charge states of qi=7 and 6. It was found that (1) the coincidence X-ray yield for (qi,qf)=(7,6) decreased faster than those for other (qi,qf) combinations, (2) the coincidence X-ray yields did not depend on the number of K-shell holes of the incident ions but on the final charge state qf.

Neutralization rate for slow Ar+ ions in front of KCl(0 0 1)

Charge state distributions of reflected ions are measured when 5keV Arq+(q=0−2) ions are incident on a clean KCl(001) surface at grazing angle, θi. Although the charge state distribution does not depend on the incident charge state at larger θi, significant dependence of the charge state distribution on incident charge state is observed at smaller θi. The ionization of Ar0 is completely suppressed at θi<20mrad, while large neutralization probability is observed for Ar+ incidence. These features allow us to derive the position-dependent neutralization rate of Ar+ in front of KCl(001). The obtained neutralization rate decreases exponentially with distance from the surface as it is usually assumed.

Cross sections for charge change in argon and equilibrium charge states of 3.5 MeV/amu uranium ions passing through argon and carbon targets

Cross sections for single and multiple electron capture and loss were measured for 3.5MeV/amu uranium ions, traveling in argon gas, as a function of incident charge state. Multiple electron loss in single collisions was found to contribute significantly to the total loss cross section. The measured cross sections were used to determine the average equilibrium charge in argon by three different methods. The resulting charges were in good agreement with each other and with the effective charge calculated from stopping powers. In order to investigate the gas–solid (density) effect on the average equilibrium charge, the charge distributions of 3.5MeV/amu uranium ions emerging from carbon foils of different thicknesses were measured. It was found that the average equilibrium charge of the uranium ions emerging from the solid is 41% larger than that of the uranium ions emerging from the gas. The energy dependences of the average equilibrium charges for uranium ions exiting carbon and argon targets were examined by combining the present results with previous results of other investigators and compared with the predictions of a semiempirical formula developed recently by Schiwietz and Grande.